Breathe deep or smoke up—it's all the same in Mumbai

Take a deep breath, then thank your lucky stars you weren't in Mumbai (unless you are, in which case, stop breathing so deeply). Breathing for a single day during Diwali, the ancient Hindu “festival of lights”, is the equivalent to smoking 113 cigarettes.

That's like smoking five packs a day for an entire week. The rise in pollution comes from the residue of firecrackers burst that happens throughout the week of Diwali. In this case, pollution is measured by the presence of Suspended Particulate Matter (SPM) that is small enough to get stuck in your lungs and provide all the nastiness that smoking causes.

A single cigarette emits 2 units of RSPM (SPM that is small enough to breathe in). An acceptable amount, according to the Pollution Control Board, is 100 units. On a normal day, without the extra firecrackers and smoke, the air contains 200 units of RSPM, equivalent to 100 cigarettes a day.

(Source)